The present invention generally relates to butt hinges, and more particularly, to an improved covered and pinned butt hinge with a slimmer appearance.
The butt hinge, also known as a mortise hinge because it is normally mortised or inset into the door jamb (frame) and into the edge of the door, is well-known in the hardware industry. Over the years, many improvements have been made to both improve its longevity and to improve its appearance. Among the developments that enhance the service life of butt hinges, particularly those used in commercial applications, is the inclusion of bearings of different kinds to reduce friction. Bronze bearings, ball bearings and friction-resistant plastic bearings have all been successfully used. Improvements in appearance have generally been limited to reducing the number of joints which occur between the interposed leaves, or reducing the size of the bearings, often at the expense of hinge performance.
The most common hinge configuration is the “five-knuckle” hinge, which is constructed from a pair of leaves and a pin around which the leaves rotate. One leaf generally has three knuckles, while its opposing leaf has two. Thrust bearings, or combinations of radial and thrust bearings are most often visible between the knuckles, adding to the complexity of the design and often compromising the appearance of the hinge. In a five knuckle hinge, either two or four bearings are used between the knuckles, depending on the service requirements of the hardware. However, only half the number of installed bearings actual carry the weight of the door, because the other two are located on those knuckle surfaces which tend to separate rather than compress when the door is installed. When such a hinge is inverted for use on doors of the opposite “hand” or swing direction, the inactive bearings will carry the weight of the door. For simplicity in manufacturing and stocking butt hinges, nearly all hinges all built to carry the door load for either right- or left-hand installations.
The history of mortise hinge development includes many attempts to refine the outward appearance of these products by reducing the number of knuckles, thereby reducing the number of unsightly joints between them. There have been designs which limit the number of knuckles to two on one leaf, and one on the other. The consequence of this design is that only one bearing is actually carrying the load for such an assembly, but bearings, if used, are always installed on both sides of the center knuckle so that the hinge can be inverted as explained above. Even more recently, butt hinges have been designed with only one knuckle on each leaf, with a bearing in between. Such hinges are thought to be a further improvement in appearance, but they must be manufactured in both left- and right-hand versions so that they can carry doors of either “hand.” This makes manufacturing and distribution more complex, because incorrect specification resulting in delays and consequential added costs often accompanies such products. Clearly, the trend toward the elimination of unsightly joints has fostered the development of butt hinges with ever-fewer knuckles, even at greater cost, inconvenience, and degradation of hinge performance.